Wireless M-Bus protocol software Status: PREVIEW

Product Information

Description

The Wireless MBUS standard (EN 13757-4:2005) specifies communications between water, gas, heat, and electric meters and is becoming widely accepted in Europe for smart metering or Advanced Metering Infrastructure (AMI) applications. Wireless MBUS is targeted to operate in the 868 MHz band. This band gives a good trade off between RF range and antenna size.

What does TI provide to help designers?

• TI has both single chip (SoC) and two chip solutions for Wireless MBUS. The two chip solution is implemented with the RF transceiver CC1101 associated with the MSP430. The system on chip solution is based on a CC1110 device with an 8051 MCU core.
• TI provides software examples to support Wireless MBUS. Application note AN067 (see "Technical documents" below) is a great starting point for developing Wireless MBUS applications. The application note describes Wireless MBUS in more detains and is accompanied by C source code examples. The code associated with this application note can be run using the MSP430 experimenters board and a CC1101 EM module. (CC1101EMK868-915 contains 2 CC1101 EMs and 2 antennas). The software example is not a full wireless MBUS stack implementation (this can be provided from TI partners), but demonstrates how the basic transmit, receive, and encoding can be performed. Optimised settings for CC1101/CC1110 and wireless MBUS is provided. The setting found will give good performance also for frequency drifting (but still within the specification) WMBUS packets. In receive mode, the kit can also work as a simple WMBUS packet sniffer displaying the raw packet data as a text string on a PC.
• TI provides low cost PCB reference antennas for this band:
  http://www.ti.com/litv/pdf/swra227a
  http://www.ti.com/litv/pdf/swru121
  http://www.ti.com/litv/pdf/swra228a

Any particular design challenges to think about?

• For the low level protocol handling, the biggest challenges with the Wireless MBUS protocol is the large data rate variation (+/-10%), the large frequency error (ppm) and a non-standard coding to remove/reduce the DC component in the data. In addition the packet format is somewhat different compared to recent RF standards. Fortunately, the packet engine and demodulator of CC1101 can handle most of the CPU intensive operations thus offloading the microcontroller. This means that CC1101 can receive data in the FIFO and wake up the MSP430 when a valid packet is being received. This feature will save power and remove the need to add complex and time critical software that would otherwise be needed to handle up to 100kbit/s over the air data rate.
• Three different performance classes of transceivers are defined in the Wireless MBUS standard and the CC1101& CC1110 comply with the highest performance class. Some implementations of WMBUS require AES encryption (128 bit keys). The CC1110 have an AES hardware engine that can handle encryption and decryption in real time.